Photocatalytic powder, photocatalytic slurry, and polymer composition, coating agent, photocatalytic functional molded article and photocatalytic functional structure using the powder

ABSTRACT

An object of the present invention is to provide a photocatalytic powder containing titanium dioxide fine particles containing an anionically active substance, where the electrokinetic potential of the fine particle is from about −100 to 0 mV in an aqueous environment at pH 5. Another object of the present invention is to provide a photocatalytic slurry containing the powder, and a polymer composition, a coating agent, a photocatalytic functional molded article and a photocatalytic functional structure using the powder.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Divisional Application of prior application Ser. No.09/839,418 filed Apr. 23, 2001, now U.S. Pat. No. 6,683,023 which is anapplication filed under 35 U.S.C. §111(a) claiming benefit pursuant to35 U.S.C. §119(e)(1) of the filing date of Provisional Application60/270,156 filed Feb. 22, 2001 pursuant to 35 U.S.C. §111(b); thedisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a material having photocatalyticactivity, more specifically, the present invention relates to aphotocatalytic powder material having photocatalytic activity, a slurrycontaining the photocatalytic powder, an organic polymer compositioncontaining the photocatalytic powder, a photocatalytic functional moldedarticle of the organic polymer composition, a coating agent comprisingthe photocatalytic slurry, and a photocatalytic functional structurehaving provided on the surface thereof the polymer composition or thecoating agent.

BACKGROUND OF THE INVENTION

In recent years, photocatalytic fine particles using titanium dioxideare attracting attention as an environmental cleaning material forantimicrobial, deodorization, antifouling, air cleaning, water cleaningand the like. The photocatalytic mechanism of titanium dioxide isconsidered attributable to the following mechanism. Upon irradiation oflight on a titanium dioxide fine particle, an electron and a hole aregenerated inside the titanium dioxide fine particle, which reacts withwater or oxygen in the vicinity of the surface of a titanium dioxidefine particle to generate hydroxy radical or hydrogen peroxide. As aresult, strong oxidation reduction activity of this hydroxy radical orhydrogen peroxide, harmful organic substances are decomposed into carbondioxide and water, and thereby cleaned. Such photocatalytic activity ofa titanium dioxide fine particle is thought to semipermanently continueas long as a titanium dioxide fine particle, light, water and oxygen arepresent.

By taking advantage of this photocatalytic property of titanium dioxide,as a representative application example, titanium dioxide fine particlesare being kneaded into an easily handleable medium, such as fiber or aplastic molded article, or into a coating on the surface of a substrate,such as cloth or paper. However, decomposition or deterioration by thestrong photocatalytic activity of titanium dioxide readily occurs notonly on harmful organic materials or environmental pollutants but alsoon the medium itself such as fiber, plastic or paper and this is anobstacle to durability in practical use. Due to easy handleability ofthe titanium dioxide fine particle, a coating material comprising amixture of titanium dioxide fine particles and a binder has beendeveloped. However, an inexpensive binder having durability sufficientlyhigh to overcome, for example, decomposition or deterioration on themedium has not yet been found.

JP-A-9-225319 (the term “JP-A” as used herein means an “unexaminedpublished Japanese patent application”) and JP-A-9-239277 disclose meansfor preventing and suppressing the deterioration of a resin medium orthe deterioration of a binder due to the strong photocatalytic activityof titanium dioxide particles. The proposed means is a method ofallowing a photo-inactive compound having such as aluminum, silicon andzirconium to be supported on a titanium dioxide particle in anarchipelago shape having a steric barrier to retard the photocatalyticactivity. According to this method, the photo-inactive compound issupported in an archipelago shape; however, specific sites of the resinmedium or the binder disadvantageously remain present under the strongphotocatalytic activity of titanium dioxide.

JP-A-10-244166 proposes a photocatalytic titanium dioxide obtained bycoating a porous calcium phosphate on the surface of titanium dioxide.However, in this case, the photocatalytic activity disadvantageouslydecreases due to the coated calcium phosphate layer.

International Publication WO99/33566 discloses a powder material oftitanium dioxide fine particles, where a porous coating layer of calciumphosphate is formed on at least a part of the surface of a titaniumdioxide fine particle and an anionic surfactant is present at theinterface therebetween.

With respect to a slurry containing titanium dioxide havingphotocatalytic activity, JP-A-10-142008 discloses an anatase-typetitanium oxide-containing slurry which is obtained by heat-treating atitania sol, a titania gel form or a titania sol-gel mixture in a closedvessel simultaneously with a pressurization treatment and thendispersing using an ultrasonic wave or stirring the treated product.

JP-A-11-343426 discloses a photocatalytic coating material havingexcellent dispersion stability and specifically discloses aphotocatalytic coating material containing, in a solvent, a silica soland titanium oxide having a Raman spectrum peak in the range of 146 to150 cm⁻¹ and being occupied by anatase type titanium dioxide in a ratioof 95% by mass or more.

Conventional techniques heretofore proposed cannot provide anindustrially useful method for producing a photocatalytic powdermaterial or slurry which can satisfy all of the photocatalytic activity,when used in combination with an organic material, durability anddispersion stability.

In view of these conventional techniques, an object of the presentinvention is to provide a photocatalytic powder material, a slurrycontaining the photocatalytic powder, an organic polymer compositioncontaining the photocatalytic powder, a molded article of the organicpolymer composition, a coating agent containing the slurry and astructure having provided on the surface thereof the organic polymercomposition or the coating agent that can effectively and profitablyperform removal of malodor, decompositional removal of harmfulsubstances or pollutants in air, water draining or cleaning treatment,or disinfectant or antifungal action (hereinafter collectively called“environmental cleaning activity”) and at the same time, have highdispersion stability, and therefore, be greatly enhanced in theindustrial utility.

Particularly, the present invention provides a photocatalytic powder anda photocatalytic slurry, which can exhibit excellent photocatalyticactivity, durability and dispersion stability when coated on the surfaceof fiber, paper or plastic material, kneaded into such a material, orused for a coating composition.

SUMMARY OF THE INVENTION

As a result of extensive investigations to attain the above-describedobjects, the present inventors have found that these objects can beattained by a photocatalytic powder material comprising a titaniumdioxide fine particle containing an anionically active substance,wherein the electrokinetic potential of the fine particle is from about−100 to 0 mV in an aqueous environment at pH 5, and by a slurrycontaining the powder.

More specifically, the present invention provides the followingembodiments.

(1) A photocatalytic powder comprising a titanium dioxide fine particlescontaining an anionically active substance, wherein the electrokineticpotential of the fine particle is from about −100 to 0 mV in an aqueousenvironment at pH 5.

(2) The photocatalytic powder as described in 1 above, wherein the fineparticle has a primary particle size of about 0.001 to about 0.2 μm.

(3) The photocatalytic powder as described in 1 or 2 above, wherein theanionically active substance is at least one substance selected from thegroup consisting of condensed phosphoric acid, organic sulfonic acid,sulfuric acid and hydrofluoric acid.

(4) An aqueous slurry containing the photocatalytic powder described isin any one of 1 to 3 above.

(5) An organic polymer composition containing the photocatalytic powderdescribed in any one of 1 to 3 above.

(6) A coating agent using the photocatalytic slurry described in 4above.

(7) An organic polymer composition comprising the photocatalytic powderdescribed in 5 above, wherein the organic polymer of the organic polymercomposition is at least one selected from the group consisting ofthermoplastic resin, thermosetting resin, synthetic resin, natural resinand hydrophilic polymer.

(8) An organic polymer composition comprising the photocatalytic powderdescribed in 5 above, wherein the organic polymer composition is anarticle selected from the group consisting of a coating material, acoating composition, a compound and a masterbatch.

(9) The organic polymer composition containing a photocatalytic powderas described in 8 above, wherein the concentration of the photocatalyticpowder in the organic polymer composition is from about 0.01 to about80% by mass based on the entire mass of the composition.

(10) A photocatalytic functional molded article obtainable by moldingthe organic polymer composition containing a photocatalytic powdermaterial described in any one of 7 to 9 above.

(11) The photocatalytic functional molded article as described in 10above, which is a molded article selected from the group consisting offiber, film and plastic.

(12) A photocatalytic functional structure having provided on thesurface thereof the photocatalytic powder described in any one of 1 to 3above.

(13) A photocatalytic functional structure having provided on thesurface thereof the coating agent described in 6 above.

(14) A coating layer comprising the photocatalytic powder described in 1or 2 above.

DESCRIPTION OF THE PRESENT INVENTION

The titanium dioxide for use in the present invention is fundamentallynot limited in the crystal form or in the production process thereof aslong as it has photocatalytic activity. For example, a titanium dioxidefine particle obtained by a vapor phase reaction starting from titaniumhalide, a titanium dioxide fine particle or sol obtained bywet-hydrolyzing a titanium halide solution, or a calcined productthereof, may be used.

The titanium dioxide fine particle for use in the present invention isnot limited in the crystal form, as described above. However, from theviewpoint of attaining high performance as a photocatalyst, anatase andbrookite are preferred. The titanium dioxide fine particle may also be acomposite crystal-system fine particle of these crystal forms orcontaining such a crystal.

The titanium dioxide for use in the present invention preferably has anaverage primary particle size of about 0.001 to about 0.2 μm, morepreferably from about 0.001 to about 0.1 μm. If the average primaryparticle size is less than about 0.001 μm, efficient production isdifficult to attain and this is not practical, whereas if it exceedsabout 0.2 μm, the photocatalytic performance of the titanium dioxidegreatly decreases.

In the present invention, it is important that the fine powder mainlycomprises the above-described titanium dioxide, that the titaniumdioxide contains an anionically active substance and that theelectrokinetic potential of the fine powder is from about −100 to 0 mVin an aqueous environment at pH 5. The term “mainly” used herein meansmore than 50%. The “anionically active substance” as used herein means asubstance having a hydrophilic atom group showing anionic property inthe molecule, the surface of which substance is readily rendered anionicin water due to its proton-donating property. Any substance satisfyingthese conditions may be used. For example, the substance having ahydrophilic atom group bearing an anion in the molecule (particularly,Bronsted acid) is at least one substance selected from the groupconsisting of condensed phosphoric acid, organic sulfonic acid, sulfuricacid and hydrofluoric acid. Examples of the condensed phosphoric acidinclude pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoricacid, trimetaphosphoric acid, tetrametaphosphoric acid andhexametaphosphoric acid. Examples of the organic sulfonic acid includemethanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid,toluenesulfonic acid and dodecylbenzenesulfonic acid. Among these,condensed phosphoric acid is preferred.

In the present invention, an anionically active substance compoundedwith titanium dioxide is present in the vicinity of the surface of afine particle, an anionically substance is adsorbed to the surface of atitanium dioxide fine particle, or an anionically active substance ispresent in the vicinity of the surface of titanium dioxide. The powdermaterial may be in any of these states.

In the present invention, the electrokinetic potential means a potentialdifference generated at the interface between a solid particle and waterin contact with each other when they perform a relative motion. Thiselectrokinetic potential is generally determined, for example, by amethod of loading an electric field to both ends of a cell containingwater having dispersed therein fine powder to cause electrophoresis andmeasuring the migration speed. For the measurement of the migrationspeed, a direct observation method through a microscope, a rotary prismmethod, a laser Doppler method, a laser rotary grating method, an imageanalysis method or a mass measuring method may be used.

Other than the electrophoresis method, a precipitation potential method,an electroosmosis method, a streaming potential method and an ultrasonicmethod may be used. Among these, an electrophoretic light-scatteringmethod is preferred, which is an electrophoresis method employing alaser Doppler speed measuring method. In the present invention, theelectrokinetic potential at pH 5 must be from about −100 to 0 mV,preferably from about −50 to about −10 mV. If the electrokineticpotential value exceeds about 0, sufficiently high photocatalyticactivity cannot be obtained and also, the dispersion stability is poor,whereas if the electrokinetic potential is less than about −100 mV,sufficiently high photocatalytic activity cannot be obtained.

In the present invention, the anionically active substance may besufficient if it is present in a ratio based on titanium dioxide suchthat the electrokinetic potential of the fine particle is from about−100 to 0 mV in an aqueous environment at pH 5. For example, theanionically active substance is preferably in a ratio of about 0.1 toabout 50 parts by mass, more preferably from about 0.2 to about 20 partsby mass, per about 100 parts by mass of titanium dioxide. If the ratioof the anionically active substance is less than about 0.1 part by mass,sufficiently high dispersion stability of the fine particle cannot beobtained, whereas if it exceeds about 50 parts by mass, the fineparticle greatly decreases in the activity as a photocatalyst. Themethod for allowing the anionically active substance to be present onthe surface of titanium dioxide is also not particularly limited. Forexample, the anionically active substance may be added in the initialstage or during the production of titanium dioxide, or the anionicallyactive substance may be added in the surface treatment step after thecompletion of the production of titanium dioxide.

In the photocatalytic powder, a metal such as platinum, rhodium,ruthenium, palladium, silver, copper and zinc may be previouslysupported on the surface of a titanium dioxide fine particle. In thiscase, the titanium dioxide fine particle is more intensified in theenvironmental cleaning activity and the disinfectant or algicidal effectis also enhanced. The metal may also be supported on the raw materialtitanium dioxide or a step of allowing the metal to be supported may beprovided in the process of incorporating the above-described anionicallyactive substance.

The slurry of the present invention is an aqueous dispersion comprisinga photocatalytic powder material which is a fine particle mainlycomprising a titanium dioxide fine particle and further containing ananionically active substance and in which the electrokinetic potentialof the fine particle is from about −100 to 0 mV in an aqueousenvironment at pH 5. A hydrophilic organic solvent may be added to thisaqueous dispersion.

The content ratio of the photocatalytic powder in the slurry is notparticularly limited but is preferably, for example, from about 0.01 toabout 50% by mass, more preferably from about 1 to about 40% by mass. Ifthe content of the photocatalytic powder is less than about 0.01% bymass, a sufficiently high photocatalytic effect may not be obtainedafter the coating, whereas if it exceeds about 50% by mass, not only aproblem such as increase in viscosity may be caused, but also isdisadvantageous in view of profitability.

A photocatalytic functional structure may be produced by adding a freelyselected binder to the above-described aqueous dispersion (slurry) toform a coating agent and coating such aqueous dispersion on the surfaceof various structures, which are described later. In the presentinvention, the binder material is not limited but, for example, at leastone selected from hydrophilic polymers, such as polyvinyl alcohol,sodium polyacrylate and poly(N-vinylacetamide), and inorganic materials,such as zirconium compound, may be used.

Examples of the zirconium compound include zirconium oxychloride,zirconium hydroxychloride, zirconium nitrate, zirconium sulfate,zirconium acetate, ammonium zirconium carbonate and zirconiumpropionate.

Specifically, the amount of the binder added to the coating agent ispreferably, for example, from about 0.01 to about 20% by mass, morepreferably from about 1 to about 10% by mass. If the content of thebinder is less than about 0.01% by mass, sufficiently high adhesion maynot be attained after the coating, whereas if it exceeds about 20% bymass, not only a problem, such as increase in viscosity, may be caused,but also is disadvantageous in view of profitability.

The photocatalytic powder of the present invention can be used as acomposition by adding it to an organic polymer. The organic polymerwhich can be used here includes thermoplastic resin, thermosettingresin, synthetic resin, natural resin and hydrophilic polymer. Byincorporating the above-described anionically active substance to thetitanium dioxide, the occurrence of the organic polymer directlycontacting the active face (surface) of the photocatalyst is reduced,and therefore, the organic polymer substrate itself is scarcely subjectto decompositional deterioration.

Examples of this organic polymer include polyethylene, nylon 6, nylon66, polyvinyl chloride, polyvinylidene chloride, polyester,polypropylene, polyethylene oxide, polyethylene glycol, polyethyleneterephthalate, silicon resin, polyvinyl alcohol, vinyl acetal resin,polyacetate, ABS resin, epoxy resin, vinyl acetate resin, cellulose,cellulose derivatives, polyamide resin, polyurethane resin,polycarbonate resin, polystyrene rein, urea resin, fluororesin,polyvinylidene fluoride, phenol resin, celluloid, chitin, starch sheet,acrylic resin, unsaturated polyester, melamine resin, alkyd resin andrayon.

The organic polymer composition containing the photocatalytic powder forenvironmental cleaning of the present invention can be used in the formof a coating material, a coating composition, a compound or amasterbatch. The concentration of the photocatalyst in the organicpolymer composition is from about 0.01 to about 80% by mass, preferablyfrom about 1 to about 50% by mass, based on the entire mass of thecomposition. In this polymer composition, an absorbent such as activatedcarbon and zeolite may be added to enhance the effect of removingmalodorous substances. In the present invention, a polymer moldedarticle having a function of cleaning the environment can be obtained bymolding the above-described polymer composition. Examples of the moldedarticle of the composition include fiber, film and plastic moldedarticle.

The polymer composition of the present invention has excellentdurability and therefore, may also be used as a coating composition fora structure such as wall material, glass, billboard or road constructionconcrete. Furthermore, when the titanium dioxide or polymer compositionof the present invention is subjected to a surface treatment, itsphotocatalytic function can be fully exhibited without causing anyphotocatalytic deterioration or destruction of the medium (structure orcoating), even if coated on a structure (organic material), such aspaper, plastic, cloth or wood, or on a body coating of a car or thelike.

EXAMPLES

The present invention is described in greater detail below by referringto the Examples, however, the present invention should not be construedas being limited to these Examples. Unless indicated otherwise herein,all parts, percents, ratios and the like are by weight.

Example 1

To 476 ml of previously weighed pure water, 0.01 g of sodiumhexametaphosphate (extra pure reagent, produced by JUNSEI CHEMICAL CO.,LTD.) was added. While stirring with a lab stirrer, the resultingmixture was heated and kept at a temperature of 98° C. Thereto, 36 g ofAqueous Titanium Tetrachloride Solution (produced by SHOWA TITANIUM CO.,LTD.) was added dropwise over 60 minutes. After the dropwise addition,the obtained white suspension was adjusted to pH 5 using anelectrodialyser. A part of the thus-obtained photocatalytic slurry wassampled and the solid concentration was measured by a dry constantweight method and found to be 2.1% by mass. The dry powder was subjectedto a structural analysis using an X-ray diffractometer, and the obtainedpowder was determined to be brookite-type titanium dioxide. Then, theobtained powder was analyzed by FT-IR (FT-IR1650, manufactured by PerkinElmer, Inc.). As a result, an absorption of metaphosphoric acid wasobserved, revealing the presence of an anionically active substance.Also, the primary particle size of the powder was determined from themeasurement results of BET specific surface area and found to be 0.015μm.

Evaluation of Photocatalytic Activity

Then, a coating solution containing 3% by mass of this powder (usingzirconium oxychloride as the binder and the amount added thereof was 20%by mass based on the powder) was prepared and coated on a commerciallyavailable glass plate by a flow coating method and on the surfacethereof, a red ink was dropped. The thus-obtained sample was placedright under a commercially available black light and after lighting ofthe light, the relative red ink discoloration rate was measured andfound to be 130.

Evaluation of Resin Deterioration

Using 10 g of the photocatalytic powder prepared above and polyethyleneterephthalate resin, a kneaded mixture having a titanium dioxideconcentration of 20% was produced at a temperature of 280° C. by meansof a commercially available batch-system kneader (Laboplasto millmanufactured by Toyo Seiki Seisaku-sho, Ltd.). From the obtainedcompound, a specimen of 3 cmφ×1 cm (“φ” used herein represents“diameter”) was manufactured using a heating press and the yellow degree(YI value according to ASTM-D1925) of the specimen was measured by aspectrocolorimeter (CM-2002, manufactured by Minolta Co., Ltd.). Changefor yellow was not observed.

Evaluation of Dispersibility

Using a part of the photocatalytic slurry, the dispersion particle sizewas evaluated by a commercially available ultrafine particle sizedistribution measuring apparatus by a laser Doppler method (UPA,manufactured by Microtrac Co., Ltd.), and found to be 0.17 μm in termsof the average particle size.

Evaluation of Electrokinetic Potential

A part of the photocatalytic slurry was sampled and measured on theelectrokinetic potential using a commercially available electrokineticpotential measuring apparatus (DELSA440, manufactured by BeckmanCoulter, Inc.) and found to be −35 mV.

Example 2

A photocatalytic powder containing an anionically active substance wasproduced in the same manner as in Example 1 except for using acidicsodium pyrophosphate (a product by TAIHEI CHEMICAL INDUSTRIAL CO., LTD.)in place of sodium hexametaphosphate. The thus-obtained photocatalyticpowder was subjected to the photocatalytic activity evaluation, theresin deterioration evaluation, the dispersion particle size evaluationand the electrokinetic potential evaluation in the same manner as inExample 1. The results obtained are shown in Table 1.

Example 3

A photocatalytic powder containing an anionically active substance wasproduced in the same manner as in Example 1 except for usingorthophosphoric acid (extra pure reagent produced by Wako Pure ChemicalIndustries, Ltd.) in place of sodium hexametaphosphate. Thethus-obtained photocatalytic powder was subjected to the photocatalyticactivity evaluation, the resin deterioration evaluation, the dispersionparticle size evaluation and the electrokinetic potential evaluation inthe same manner as in Example 1. The results obtained are shown in Table1.

Example 4

In a 1 L-volume flask, 476 ml of pure water was weighed, heated whilestirring with a lab stirrer and kept at a temperature of 98° C. Thereto,36 g of Aqueous Titanium Tetrachloride Solution (produced by SHOWATITANIUM CO., LTD.) was added dropwise over 60 minutes. After thedropwise addition, the obtained white suspension was adjusted to pH 5using an electrodialyser. To this solution, 0.1 g of sodiumhexametaphosphate (extra pure reagent, produced by JUNSEI CHEMICAL CO.,LTD.) was added. The resulting slurry was charged into a 2.4 L-volumepot mill previously filled with 2 kg of zirconia beads of 0.8 mm andmixed at a rotational frequency of 100 rpm to obtain a photocatalyticslurry containing an anionically active agent. A part of this slurry wassampled and the solid concentration was measured by a dry constantweight method and found to be 1.9% by mass. The dry powder was subjectedto a structural analysis using an X-ray diffractometer, and the obtainedpowder was brookite-type titanium dioxide. Then, the obtained powder wasanalyzed by FT-IR (FT-IR1650, manufactured by Perkin Elmer, Inc.), andan absorption of metaphosphoric acid was observed, revealing thepresence of an anionically active substance.

Comparative Example 1

In a 1 L-volume flask, 476 ml of pure water was weighed, heated whilestirring with a lab stirrer and kept at a temperature of 98° C. Thereto,36 g of an aqueous titanium tetrachloride solution (produced by SHOWATITANIUM CO., LTD.) was added dropwise over 60 minutes. After thedropwise addition, the obtained white suspension was adjusted to pH 5using an electrodialyser. A part of this slurry was sampled and thesolid concentration was measured by a dry constant weight method andfound to be 2.1% by mass. The dry powder was subjected to a structuralanalysis using an X-ray diffractometer, and the obtained powder wasbrookite-type titanium dioxide. Also, the primary particle size of thepowder was determined from the specific surface area measured by a BETmethod and found to be 0.016 μm. Subsequently, the photocatalyticactivity evaluation and the resin deterioration evaluation of thepowder, and the dispersion particle size evaluation and theelectrokinetic potential evaluation of the slurry were performed in thesame manner as in Example 1. The results obtained are shown in Table 1.

Comparative Example 2

To 499 ml of pure water, 1 g of a commercially available photocatalyticpowder material (ST-01, produced by Ishihara Sangyo Kaisha, Ltd.) wasadded, and the resulting mixture was dispersed by a lab stirrer toobtain a photocatalytic slurry. Using original powder, thephotocatalytic activity evaluation and the resin deteriorationevaluation were performed in the same manner as in Example 1. Also,using the photocatalytic slurry obtained above, evaluations ofdispersion particle size and electrokinetic potential were performed inthe same manner as in Example 1. The results obtained are shown in Table1.

Comparative Example 3

To 499 ml of pure water, 1 g of a commercially available titaniumdioxide for pigment (A220, produced by Ishihara Sangyo Kaisha, Ltd.) wasadded, and the resulting mixture was dispersed by a lab stirrer toobtain a photocatalytic slurry. To this solution, 0.1 g of sodiumhexametaphosphoric acid (extra pure reagent produced by JUNSEI CHEMICALCO., LTD.) was added. The resulting slurry was charged into a 2.4L-volume pot mill previously filled with 2 kg of zirconia beads of 0.8mm and mixed at a rotational frequency of 100 rpm to obtain aphotocatalytic slurry containing an anionically active agent. A part ofthis slurry was sampled and the solid concentration was measured by adry constant weight method and found to be 1.9% by mass. Using the drypowder obtained here, the photocatalytic activity evaluation and theresin deterioration evaluation were performed in the same manner as inExample 1. Also, using the photocatalytic slurry obtained above,evaluations of dispersion particle size and electrokinetic potentialwere performed in the same manner as in Example 1. The results obtainedare shown in Table 1.

Comparative Example 4

A photocatalytic powder material and a photocatalytic slurry wereobtained in the same manner as in Example 1 except for changing theamount added of sodium hexametaphosphate to 0.001 g. Evaluations ofphotocatalytic activity, resin durability, dispersion particle size andelectrokinetic potential were performed in the same manner as inExample 1. The results obtained are shown together in Table 1.

Comparative Example 5

A photocatalytic powder material and a photocatalytic slurry wereobtained in the same manner as in Example 1 except for changing theamount added of sodium hexametaphosphate to 0.7 g. Evaluations ofphotocatalytic activity, resin durability, dispersion particle size andelectrokinetic potential were performed in the same manner as inExample 1. The results obtained are shown together in Table 1.

TABLE 1 Anionically Photo- Primary Dispersion Electrokinetic ActiveCatalytic Particle Particle Resin Potential Agent Activity Size (μm)Size (μm) Durability (mV) Example 1 Present 130 0.015 0.17 ◯ −35 2Present 120 0.016 0.19 ◯ −33 3 Present 115 0.016 0.20 ◯ −28 4 Present122 0.015 0.18 ◯ −34 Comparative None 95 0.016 Immeasurable X 30 Example1 2 None 80 0.008 0.65 X 27 3 None 10 0.15 0.78 ◯ 29 4 Present 96 0.0150.54 X 5 5 Present 98 0.015 0.25 ◯ −105 ◯: In the yellow degree test ofresin, change for yellow was not observed. X: In the yellow degree testof resin, change for yellow was observed.

The photocatalytic powder and slurry of the present invention are auseful material capable of effectively and profitably performing removalof malodor, decompositional removal of harmful substances or pollutants,water draining or cleaning treatment, or antibacterial or antifungalaction. Also, the slurry of the present invention containing thephotocatalytic powder has excellent dispersion stability, and therefore,utility in industry is greatly enhanced. Particularly, the presentinvention can provide a catalytic powder material and a catalyticslurry, which exhibit excellent photocatalytic activity, durability anddispersion stability when coated on the surface of fiber, paper orplastic material, kneaded into such a material, or used for a coatingmaterial composition.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

1. A photocatalytic powder comprising titanium dioxide fine particlescomprising an anionically active substance, wherein the fine particleshave an electrokinetic potential of from about −100 mV to −10 mV in anaqueous environment at pH 5, and wherein the crystal form of thetitamium dioxide fine particles is brookite.
 2. The photocatalyticpowder according to claim 1, wherein the fine particles have a primaryparticle size of about 0.001 to about 0.1 μm.
 3. The photocatalyticpowder according to claim 1, wherein the anionically active substance isat least one substance selected from the group consisting of condensedphosphoric acid, organic sulfonic acid, sulfuric acid and hydrofluoricacid.
 4. An aqueous slurry comprising water and the photocatalyticpowder claimed in claim
 1. 5. A coating agent comprising a binder andthe aqueous slurry claimed in claim
 4. 6. A photocatalytic functionalstructure comprising a structure having provided on the surface thereofthe coating agent claimed in claim
 5. 7. The photocatalytic functionalstructure according to claim 6, wherein the structure is selected fromthe group consisting of paper, plastic, cloth, wood, body coating of acar, wall material, glass, billboard and road construction concrete. 8.An organic polymer composition comprising an organic polymer and thephotocatalytic powder claimed in claim
 1. 9. A photocatalytic functionalmolded article obtained by molding the organic polymer compositionclaimed in claim
 8. 10. The organic polymer composition according toclaim 8, wherein the organic polymer is at least one polymer selectedfrom the group consisting of polyethylene, nylon 6, nylon 66, polyvinylchloride, polyvinylidene chloride, polyester, polypropylene,polyethylene oxide, polyethylene glycol, polyethylene terephthalate,silicon resin, polyvinylalcohol, vinyl acetal resin, polyacetate, ABSresin, epoxy resin, vinyl acetate resin, cellulose, cellulosederivatives, polyamide resin, polyurethane resin, polycarbonate resin,polystyrene resin, urea resin, fluororesin, polyvinylidene fluoride,phenol resin, celluloid, chitin, starch sheet, acrylic resin,unsaturated polyester, melamine resin, alkyd resin and rayon.
 11. Theorganic polymer composition according to claim 10, wherein thecomposition further comprises activated carbon and/or zeolite.
 12. Aphotocatalytic functional structure comprising a structure havingprovided on the surface thereof the photocatalytic powder claimed inclaim
 1. 13. The photocatalytic functional structure according to claim12, wherein the structure is selected from the group consisting ofpaper, plastic, cloth, wood, body coating of a car, wall material,glass, billboard and road construction concrete.
 14. A coating layercomprising the photocatalytic powder claimed in claim
 1. 15. Thephotocatalytic powder according to claim 1, wherein metals are supportedon the surface of the titanium dioxide fine particles.
 16. Thephotocatalytic powder according to claim 15, wherein the metal comprisesat least one metal selected from the group consisting of platinum,rhodium, ruthenium, palladium, silver, copper and zinc.
 17. Aphotocatalytic powder comprising titanium dioxide fine particlescomprising an anionically active substance, wherein the fine particleshave an electrokinetic potential of from about −100 mV to −10 mV in anaqueous environment at pH 5, and wherein the titanium dioxide fineparticles is a composite crystal-system of anatase and brookite.